Vitamin D2 (ergocalciferol) is found naturally in only one significant food source: mushrooms. Beyond that, it shows up in fortified foods like plant milks, orange juice, and some breakfast cereals. Unlike vitamin D3, which comes from animal sources and sunlight, D2 is plant-derived, making it especially relevant for people following vegan or vegetarian diets.
Mushrooms Are the Only Major Natural Source
Mushrooms are unique in the food world because they produce vitamin D2 the same way human skin produces D3: through UV light exposure. When mushrooms are hit with ultraviolet light, they convert a compound called ergosterol into vitamin D2. This makes them the only non-fortified, non-animal food with meaningful amounts of vitamin D.
The catch is that most commercially grown mushrooms never see sunlight. They’re raised in dark, climate-controlled environments, so their vitamin D2 content is negligible. USDA testing found that untreated portobello mushrooms contained just 10 to 11 IU per 100 grams, which is essentially nothing. Crimini, enoki, oyster, shiitake, and white button mushrooms tested similarly low unless they’d been accidentally exposed to light during processing.
UV-treated mushrooms tell a completely different story. Portobello mushrooms exposed to UV light for just 15 to 20 seconds jumped to around 446 IU per 100 grams, a roughly 40-fold increase. Results varied by producer, ranging from 140 IU to 752 IU per 100 grams, but even the low end is a substantial amount. Many grocery stores now sell mushrooms labeled “UV-exposed” or “high in vitamin D” for this reason.
You Can UV-Treat Mushrooms at Home
If you can’t find UV-treated mushrooms at the store, placing regular mushrooms gill-side up in direct sunlight for 15 to 30 minutes significantly boosts their D2 content. This works with any variety. The conversion happens quickly and the vitamin D2 remains stable in the mushroom tissue after sun exposure.
Fortified Foods With Vitamin D2
Most of the vitamin D2 in the average diet comes not from mushrooms but from fortified foods. Manufacturers add D2 to products that don’t naturally contain vitamin D, particularly plant-based products. While some brands use D3 instead (sometimes derived from lanolin, an animal product), D2 remains common in vegan-friendly options. Check the label to confirm which form a product uses.
Here’s what typical fortification looks like per serving:
- Soy milk: about 119 IU per cup
- Almond milk: about 107 IU per cup
- Oat milk: similar range to other plant milks, though amounts vary by brand
- Fortified orange juice: about 100 IU per 8-ounce glass
- Breakfast cereals: varies widely by brand, typically 40 to 100 IU per serving
None of these individually comes close to a full day’s requirement, but combining a couple of fortified foods with UV-treated mushrooms can add up meaningfully.
How Much Vitamin D You Actually Need
The recommended daily amount of vitamin D (combining D2 and D3) depends on your age. Most adults need 600 IU (15 mcg) per day. Adults over 71 need 800 IU (20 mcg). Infants need 400 IU, and children and teens need 600 IU. These numbers come from the NIH and apply to both forms of vitamin D.
To put that in perspective, a cup of fortified soy milk covers about 20% of an adult’s daily need. A serving of UV-treated portobello mushrooms (roughly 100 grams, or about one large cap) could cover 75% or more, depending on the intensity of UV exposure.
D2 vs. D3: Does the Form Matter?
Vitamin D2 works, but it’s not quite as effective as D3 at raising and maintaining your blood levels of vitamin D. A meta-analysis published in the journal Nutrients found that D3 raised total vitamin D blood levels by about 15.7 nmol/L more than D2 across multiple studies. D2 has a slightly shorter half-life in the bloodstream (about 14 days compared to 15 days for D3), and it binds less efficiently to the proteins that transport vitamin D through your body.
That said, the gap narrows with daily intake. The difference between D2 and D3 is most pronounced when people take large, infrequent doses (like a weekly or monthly supplement). With consistent daily intake from food, D2 performs closer to D3. So if you’re eating D2-rich foods regularly, the lower potency is less of a concern than the headlines might suggest.
Cooking and Vitamin D2 Retention
Cooking does reduce the vitamin D2 in mushrooms, but not dramatically. Research from the Technical University of Denmark tested several cooking methods on button mushrooms and found retention rates between 62% and 89%. Boiling for 20 minutes preserved the most, while pan-frying and oven-baking at higher temperatures caused slightly more loss. Even in the worst case, you’re keeping well over half the vitamin D2, which is better than many heat-sensitive vitamins. The practical takeaway: cook your mushrooms however you like without worrying too much about destroying the vitamin D.
Putting It All Together
If you’re specifically trying to get vitamin D2 from food, your strategy is straightforward. UV-treated mushrooms are far and away the richest natural source, potentially delivering several hundred IU in a single serving. Fortified plant milks, cereals, and orange juice fill in the gaps with smaller but consistent amounts. For people who eat animal products, D3 sources like fatty fish and egg yolks are more efficient at raising blood levels, but for vegans and vegetarians, a combination of UV-exposed mushrooms and fortified foods is a practical way to meet daily needs without supplements.